Saharan dust and Amazon freshwaters cause algal blooms

Publication date: Friday 20 October 2017

Category: DUST

New findings suggest that both Saharan dust and freshwater from the Amazon may have led to algal blooms in the western equatorial Atlantic Ocean. Those are the conclusions of a new paper published by Catarina Guerreiro and colleagues in the open-access journal Biogeosciences.

The conclusions were drawn after an extensive study of assemblages of tiny [about 5µm (1µm = 1/1000 mm)] calcite platelets produced by coccolithophores (calcareous nannoplankton) that live in the photic layer of the ocean, collected with sediment traps that were deployed between Africa and the Caribbean, directly below the main Saharan dust plume at 12oN. It turns out that especially in the western parts of the Atlantic Ocean, the algae respond to input of both fresh water from the Amazon River, as well as to deposition of dust blown in from the Sahara Desert.

Why are we so interested in dust?

It turns out that there are many direct and indirect links between dust and climate. The most straightforward one is fine-grained dust in the upper atmosphere blocking incoming sunlight, causing a net cooling effect. But there are warming effects too; in the lower atmosphere, coarser-grained dust particles absorb energy that was refelected at the earth's surface and this way, dust acts as a greenhouse gas.

There are many more negative and positive climate-related effects but the main link to the ocean is the fact that marine life may profit from nutrients in dust. When plankton reproduces, it takes up CO2 from the atmosphere. Thus, dust could potentially act as an ocean fertilizer, sequestering a greenhouse gas!